80 . S. GOTO. 



bipolar cells, but, there are also among them multipolar cells ( PI. XXIV, 

 fig. 5); and unlike what is seen in the other genera, the fibres proceed- 

 ing from them can be very distinctly followed for a .considerable 

 distance. These fibres are direct continuations of the protoplasm of 

 the cells, are destitute of any sheath, and run in the long direction of 

 the brain, i. e., at right angles to the long axis of the body. They 

 stain quite deeply near the nucleus, but become fainter and fainter 

 as we follow them away from the nucleus, until they finally, in their 

 affinity for stains, become scarcely distinguishable from the fluid which 

 fills the meshes of the connective tissue. 



In the brain are imbedded the eyes, when such are present. 

 Among the genera I have studied, these are present only in Tristomum, 

 E-pibclella, and Monocotijle, and are arranged in two pairs. In all the 

 three genera just mentioned, their relative positions are such that an 

 isosceles trapezoid is formed by connecting them. In Tristomum and 

 Epibclella, the shorter of the two parallel sides of the trapezoid is 

 situated anteriorly, while in Monocotijle the reverse is the Case. I have 

 carefully studied these eyes only in Tristomum ovale ; and my results 

 are somewhat different from those arrived at by Lang.'^ This 

 writer enumerates four elements of which a single eye is formed, viz., 

 (1) the pigment, (2) the lens, (3) the retina, and (4) the ocular 

 muscle. According to my observation the last is no other than the 

 dorso- ventral muscles of the body which traverse the brain close to 

 the eyes, and it therefore seems to me morphologically more con'ect 

 to call them by that name, although physiologically they take great 

 part in the movements of the eyes, which are merely passive, the 

 worm having no power to direct its eyes in any special direction. 

 In the anterior eye (PI. XXIV, fig. 3) the lens is an ellipsoidal, 



1). I. V. p. 41. 



